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My friend is looking at one of these that says this "Calibration manual at 2 points with 1 set of memorized buffers (pH 4.01 / 7.01)". Would it be necessary to purchase calibration solution if it has a set of memorized buffers? He's not familiar with these things and neither am I, so any information at all on these would be great. This one is water-proof, has an automatic temperature compensation feature, and is 50 euros ($75). Any thoughts/experience?

i believe when it says memorized buffers, that means those are the two buffer pHs that it needs to calibrate and generate its standard curve. it's not that it has them memorized per say, just that it will probably explicitly ask for those two specific pHs during calibration.

if letting it sit overnight, or longer than a few hours in general, you should always recalibrate before taking another measurement. make sure to store it with care, usually in an aqueous solution, while you're not working with it.

an automatic temperature compensation eh? sounds badass. i have to do all my calibrations and readings at room temp. just for accuracy's sake, i would suggest doing the same with any solutions your friend measures. just let the standards and unknown sit in the same room for a bit so there's not too much of a temp difference.

--------------------"Prohibition will work great injury to the cause of temperance. It is a species of intemperance within itself, for it goes beyond the bounds of reason in that it attempts to control a man's appetite by legislation, and makes a crime out of things that are not crimes. A Prohibition law strikes a blow at the very principles upon which our government was founded." - Abraham Lincoln

"There are a thousand hacking at the branches of evil
to one who is striking at the root"
~ Henry D. Thoreau
Strike The Root

Quote:Yrat said:i believe when it says memorized buffers, that means those are the two buffer pHs that it needs to calibrate and generate its standard curve. it's not that it has them memorized per say, just that it will probably explicitly ask for those two specific pHs during calibration.

Makes sense. Luckily that solution isn't very expensive. How many readings do you think a 20ml pouch will provide for (one 20ml pouch for each calibration point, of course)?

Quote:

if letting it sit overnight, or longer than a few hours in general, you should always recalibrate before taking another measurement. make sure to store it with care, usually in an aqueous solution, while you're not working with it.

Would it be necessary to buy rinse solution as well? That stuff is a little bit more expensive.

Quote:

an automatic temperature compensation eh? sounds badass. i have to do all my calibrations and readings at room temp. just for accuracy's sake, i would suggest doing the same with any solutions your friend measures. just let the standards and unknown sit in the same room for a bit so there's not too much of a temp difference.

what we do here is keep the standards in small glass vials. these keep almost indefinitely as long as you rinse in between switching solutions. you dont want to bring standard buffer into your unknown, or pH 4 into pH 7 etc etc. as for a rinse solution, we just use ddH20. it's just distilled, dionized, absolutely pure water. buy some from walmart and put it in a squirt bottle, and just squirt down the probe in between different solutions. i also just wipe it down with a kim-wipe to make sure i don't dilute the standards over time with the drops of water that stay behind after washing.

--------------------"Prohibition will work great injury to the cause of temperance. It is a species of intemperance within itself, for it goes beyond the bounds of reason in that it attempts to control a man's appetite by legislation, and makes a crime out of things that are not crimes. A Prohibition law strikes a blow at the very principles upon which our government was founded." - Abraham Lincoln

"There are a thousand hacking at the branches of evil
to one who is striking at the root"
~ Henry D. Thoreau
Strike The Root

I use a calibration solution, it just makes sense because they will need calibration. The pH meter I bought recently made me lose a week of vegging because it need to be recalibrated. It had to be recalibrated everyday for the first week then worked, if I didn't have the pH buffer solution I would have been fucked because my nutrient is too dark to use those color changing drops that GH and other companies make. There are some good pH meters on eBay that come with buffer solutions and are only 30 bucks for everything. I've used both Milwaulki brand and Hanna, I prefer the Hanna although it broke after dropping it once so don't drop it.

pH meters measure a proton gradient across a glass membrane between an inner solution and outer unknown solution. over time, and during storage, this gradient will drift until equilibrium is reached with the solution it is being stored in. this is why calibration needs to be repeated before every measurement.

--------------------"Prohibition will work great injury to the cause of temperance. It is a species of intemperance within itself, for it goes beyond the bounds of reason in that it attempts to control a man's appetite by legislation, and makes a crime out of things that are not crimes. A Prohibition law strikes a blow at the very principles upon which our government was founded." - Abraham Lincoln

"There are a thousand hacking at the branches of evil
to one who is striking at the root"
~ Henry D. Thoreau
Strike The Root

Quote:Yrat said:what we do here is keep the standards in small glass vials. these keep almost indefinitely as long as you rinse in between switching solutions.

Digging up this topic because I have more questions. Most of them are going to have to wait until I'm back home and can post pictures, because I'm hoping you'll be able to help me with calibration, since the instructions for my pH meter are only in Italian. It seems that the top of the instrument has a cap that you remove and it came with a small needle that gets touched on something in there in order to calibrate. Does this sound familiar? I didn't take too much time to investigate because there was plenty of other things for the grow to check out.

In the meantime though, do you store the standards in room-temperature or do they need to be refrigerated? We didn't spring for the rinse solution that was being sold because of the price, but I'm assuming that RO water should work decently enough; any difference should be more subtle and not too consequential as far as an informal grow is concerned, right?

the needle may be to fill the inner reservoir with the inner reference electrode solution, usually silver chloride and/or potassium chloride. pictures will definitely help though.

the standards should be stored at room temp. this will give you the proper calibration, as readings will change with variations in temperature. just make sure the solution you're measuring is also at room temp so it falls on the same curve generated by the calibration. RO water is fine for rinsing, rinse and dry with a wipe between calibration solutions, and also before going into your unknown soln. you'll also want to store the electrode in some sort of aqueous buffer, maybe a bit of RO water with a few drops of the pH 7.0 standard, between readings. you don't want to let it dry out.

--------------------"Prohibition will work great injury to the cause of temperance. It is a species of intemperance within itself, for it goes beyond the bounds of reason in that it attempts to control a man's appetite by legislation, and makes a crime out of things that are not crimes. A Prohibition law strikes a blow at the very principles upon which our government was founded." - Abraham Lincoln

"There are a thousand hacking at the branches of evil
to one who is striking at the root"
~ Henry D. Thoreau
Strike The Root

--------------------"Prohibition will work great injury to the cause of temperance. It is a species of intemperance within itself, for it goes beyond the bounds of reason in that it attempts to control a man's appetite by legislation, and makes a crime out of things that are not crimes. A Prohibition law strikes a blow at the very principles upon which our government was founded." - Abraham Lincoln

"There are a thousand hacking at the branches of evil
to one who is striking at the root"
~ Henry D. Thoreau
Strike The Root

To calibrate, there is this tiny little screw by the batteries, and after you put it in the 7.01 calibration solution, you just turn the screw a little bit to adjust it, if necessary, to get it on 7.0. It actually only calibrates to 7.01, and not 4.01 as well, meaning that the description on the website was fucked. It seems to work quite well, as far as I can tell. It just went through a marathon session of coco flushing to get it to 5.5. It remembers its calibration well after measuring higher and lower pH levels, multiple runs through (not really necessary to check calibration after every reading in the same session). The readings of various things have stayed consistent, so as long as the pH it says it is, is actually the numbers it is supposed to be, then everything is great.